Aircraft utilize a protective coating system that is applied to the aircraft to minimize corrosion and resistance of the exterior surface of an aircraft and to provide the desired color, infrared properties, impact resistance, and gloss to the exterior surface. Current protective coating systems often consist of a primer and a separate topcoat film, both individually applied to the aircraft. Primer coatings that meet current military specifications typically are epoxy resins pigmented with strontium chromate for corrosion protection. Topcoats that meet current military specifications typically are polyurethane resins with appropriate pigmentation to provide color, infrared properties, and low gloss.
However, such protective coating systems suffer from several distinct drawbacks. Corrosion inhibitors containing chromium (VI) compounds, such as strontium chromate, are widely and effectively used to control corrosion of aluminum alloys, such as those used to make military aircraft. However, while these chromium compounds have excellent corrosion protective and inhibitive properties, they are toxic and suspected carcinogens. Compliance with current environmental, safety and health regulations relating to chromium use is expensive. As trends to increase the stringency of occupational health and environmental regulations continue, the use of chromium may no longer be feasible.
In addition, high performance coating systems typically contain volatile organic compounds (VOCs), which result in the production of smog, and hazardous air pollutants (HAPs) such as methyl ethyl ketone (MEK), toluene, and xylene. Standards for emissions continue to become stricter. Accordingly, the indefinite continuation of current technology utilizing compounds that release VOCs and HAPs is not only undesirable, but may not be possible in the future.
The above-described coatings also are logistically and operationally undesirable. A key area of concern in the aerospace/military industry is cycle time reduction for systems applications. It is also desirable for coating systems to be easily and quickly repairable in the event of damage. However, the current coating systems require the application of two separate coatings, the primer and the topcoat. In addition, the curing time for current aerospace/military coatings can be as long as 72 hours or more, significantly reducing the operation availability of the aircraft.
Accordingly, it is desirable to provide a protective corrosion-resistant coating for military and commercial aircraft and spacecraft that does not utilize chromium or chromium compounds and that releases minimal or no VOCs or HAPs. In addition, it is desirable to provide a protective coating for military and commercial aircraft and spacecraft that can be applied and cured quickly. It is also desirable to provide a method for painting an aircraft with such a protective coating system. Furthermore, other desirable features and characteristics of the chrome-free, self-priming coating will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.